Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.40	7.726%	$89.8435	$89.84	$89.85	$89.80
Purchase #2	$104.32	6.826%	$111.4409	$111.44	$111.45	$111.40
Purchase #3	$105.38	3.290%	$108.847	$108.85	$108.85	$108.80
Purchase #4	$146.97	11.743%	$164.2287	$164.23	$164.25	$164.20
Purchase #5	$139.64	7.418%	$149.9985	$150.00	$150.00	$150.00
Purchase #6	$32.55	9.550%	$35.6585	$35.66	$35.65	$35.70
Purchase #7	$33.39	12.217%	$37.4693	$37.47	$37.45	$37.50
7 purchase totals =	$645.65		$697.4864	$697.49	$697.50	$697.40